This invention relates to a disc drive assembly and, more particularly, to apparatus used with that assembly for maintaining proper pressure within the housing thereof.
Disc drive apparatus are known wherein a rapidly rotating "rigid" magnetic disc has information written thereon and read therefrom. Typically, such disc drive apparatus, also known as Winchester Drive disc systems, are provided with one or more discs having diameters on the order of 14 inches, 8 inches, 51/4 inches and, more recently, 31/2 inches. A conventional disc drive assembly is described in, for example, U.S. Pat. No. 4,418,369, assigned to the assignee of the present invention.
In the disc drive assembly described in the aforementioned patent, two magnetic discs are provided in a substantially sealed housing. Information is written onto each disc and read therefrom in digital form by means of a so-called "flying head". The head, or magnetic transducer, moves across the surface of the disc in a generally radial direction to write or read information on selected tracks. Movement of the head is provided in accordance with, for example, U.S. Pat. No. 4,428,012, also assigned to the assignee of the present invention. Preferably, in disc drive assemblies of the aforementioned type, information is written on and read from both surfaces of each disc. Thus, four heads may be used with a two-disc assembly.
As is conventional, in the usual disc drive assembly using one, two or more discs, such discs rotate in the environment of a gas, such as air. The housing of the assembly preferably is sealed to prevent contaminants from entering and interfering with the proper writing and reading of data on the discs. However, for various reasons, it is desirable to vent the sealed housing to ambient air. To this effect, filters have been employed successfully to prevent foreign particles from entering into the housing through the venting apparatus.
By reason of the rotation of the discs within the housing, a so-called pressure profile is established therewithin. In the absence of impellers or the like, the mere rotation of the discs inherently causes air to flow through the housing in the general direction of rotation so as to establish a relatively lower pressure at the vicinity of the disc-drive spindle. The pressure increases in the radial direction, resulting in a greater pressure at the outer periphery of the discs.
Typically, and as described in aforementioned U.S. Pat. No. 4,418,369, the disc-drive motor is disposed externally of the sealed housing. Consequently, a "spindle seal" is required to prevent contaminants from entering the housing by way of the opening therein through which passes the drive spindle. It had been thought that the interior pressure of the housing in the direct vicinity of the spindle should exhibit a maximum pressure to prevent contaminants from leaking into the assembly in the event that the spindle seal deteriorates over a period of time. However, as mentioned above, the interior pressure at the vicinity of the spindle due to the rotation of the discs generally is relatively low, and may be less than the ambient pressure. Accordingly, prior art techniques provided means, usually an impeller, a flow obstruction or the like, to increase this pressure to be greater than ambient In U.S. Pat. No. 4,418,369, ambient pressure is supplied directly to the vicinity of the spindle by way of a conduit that communicates with the exterior of the sealed housing via a filter. Hence, the pressure across the spindle seal is essentially balanced because ambient pressure is applied to both sides (i.e. both the interior and exterior pressures are substantially equal to ambient).
The present invention functions to prevent or at least minimize deterioration of the spindle seal and provide positive pressure in the disk drive assembly by way of another technique.